The present invention relates to optical sights, in particular to an optical gun sight with reticle patterns switchable for adaptation to various shooting conditions. More specifically, the invention relates to an optical sight, such as, e.g., a gunsight or a camera viewfinder, in which reticle patterns are switched electronically without mechanical movements.
Optical sights are used in viewfinders for aiming photocameras or in firearms for accurate aiming of rifles, pistols, shotguns and the like. In firearms, these optical sights are typically mounted in an elongated tubular barrel or housing carrying conventional ocular and objective lens systems. An erector-lens system is provided between the ocular and objective systems to provide an erect target image for viewing by the shooter. Windage and elevation adjustments permit the sight to be compensated for targets at varying ranges.
For example, a conventional optical sight includes a reticle, typically of cross hair or post form, which is seen by the shooter in silhouette and superimposed over the target image. The position of the firearm is adjusted until the reticle is positioned on a target-image aiming point. The primary advantage of an optical sight is that the target image and reticle are in the same focal plane, eliminating any need for the shooter to shift eye focus between sight and target as must be done with conventional open sights on a rifle. The optical sight may provide fixed or variable magnification of the target image, but such magnification is not an essential feature and is subsidiary to the primary goal of providing a target image and aiming reticle in a single focal plane.
Conventional reticles are highly satisfactory during conditions of full daylight, but most hunting for game animals is done under restricted lighting conditions before sunrise or just before dark. This is because most game animals are nocturnal feeders, and their search for food is made in darkness or in the relatively short periods just before or after full darkness. A conventional optical sight is difficult to use in these conditions of subdued lighting because the reticle is seen in silhouette against a low-contrast dimly lit image of the target and target background. It is not uncommon for a hunter to lose sight of the reticle entirely while attempting to aim at a game animal standing or moving against a dark background of brush or trees. In such conditions, the firearm cannot be accurately sighted, and the animal will probably escape.
The xe2x80x9cfading reticlexe2x80x9d problem is solved by illuminating the reticle itself (e.g., electrically heated incandescent reticles have been proposed), or preferably by providing a luminous dot or other mark at the aiming point of the sight. Details of the latter solution are shown in U.S. Pat. No. 3,672,782 issued in 1972 to A. Akin. This patent shows a an optical sight with a battery-operated internal lamp, which projects a luminous reticle pattern (dot, cross hair, circle, etc.) on the sight field of view and centered on the sight aiming point. The optical sight of this patent is provided with multiple reticles, which can be selectively switched to a working position in compliance with the shooting conditions. This is achieved with the use of a flexible strip of a plastic material wound on extends between a pairs of shafts. The strip is generally opaque but defines specific transparent zones forming a plurality of reticles. Rotation of the shafts moves strips in certain fashion within a chamber in the mounting leg, and rotation is continued until a selected reticle is positioned for projection onto an ocular focal plane of the sight. Positions of the reticles are fixed with the use of spring-loaded knobs.
A disadvantage of the device of U.S. Pat. No. 3,672,782 consists in that the sight contains moveable parts and that the strip moves back and forth. Such a system, normally, has significant plays, which impair positioning of the reticles in the focal plane, and thus impairs accuracy of shooting.
U.S. Pat. No. 4,554,744 issued in 1985 to C. Huckenbeck is directed to an improved illuminated-reticle optical sight having a very compact battery-housing and actuating-switch assembly, which enhances the styling of the instrument, and is simple and convenient for the shooter to use. Though the optical sight of this device does not have moveable parts, it also does not have selectivity of reticles.
U.S. Pat. No. 4,618,221 issued in 1986 to R. Thomas describes an adjustable telescopic sight having objective lenses, intermediate lenses, and an eyepiece. The sight is provided with an adjustable reticle device, which is disposed in the second focal plane intermediate, the eyepiece and the intermediate lenses. The adjustable reticle device is provided with a fixed centerline reticle and two identical moveable reticles located on opposite sides of the centerline reticle. The moveable reticles are each supported by a carrier, which is moveable in two orthogonal directions by means of two threaded stems carried by the body of the adjustable reticle device. The stems are each provided with knurled knobs, each of which has two arrows thereon disposed at right angles to each other on the side of the knob facing the shooter so that the shooter can readily determine the direction of movement of bullet impact upon rotation of a knob in any specific direction.
Although this device is capable of adjusting position of a reticle with relatively high accuracy due to micrometric movements and of selecting reticles of a few types, the choice of reticles is very limited and the adjustment is carried out due to movement of reticle parts.
International Patent Publication WO 00/50836 of Aug. 31, 2000 issued to K. Gunnarsson, et al. describes an optical sight with a reticle produced by projecting a reticle image from a transparent media onto a concave semitransparent mirror. The source of light is a light emitting diode (LED), which is located on a sidewall within a tubular casing of the optical sight. The LED, the transparent media with the reticle image, the semitransparent concave mirror, and the eye of the viewer form an optical system, in which the reticle image is reproduced on the eye retina, while the image of the reticle is located on the optical axis of the optical system and is seen by the eye as if it is located in the infinity or in a very remote zone. During shooting, the reticle is aligned with the image of the target, which is also seen by the viewer""s eye. Such a system ensures accurate aiming and is free of moveable parts. Furthermore, the sight of the type disclosed in WO 00/50836 is a sight of a collimating type, which does not have an optical eyepiece on the viewer""s side and therefore has a not limited eye relief. An eye relief is a distance from the viewer eye to the sight. However, this system has only one reticle and cannot be adjusted for different shooting conditions.
In order to solve the above problem, American Technologies Network Corporation, South San Francisco, Calif., has developed an optical sight of the type described in WO 00/50836, but with a turret head that contains a plurality of reticle images, which can be selectively switched to a position aligned with the optical axis by rotating the turret head. Such a system makes it possible to select reticles in compliance with the shooting conditions, shooter""s vision conditions, shooter""s hunting habits, type of the target, etc. Nevertheless, the turret-type reticle switching mechanism has moveable parts and therefore has inevitable plays in the rotary mechanism. Since the image of the reticle is projected to the infinity and is seen as a virtual image, even slightest deviations of the reticle image projection from the optical axis will impair accuracy of shooting.
Thus, all known switchable optical sights of the types described above cannot ensure stability in positioning of the reticle with respect to the center of the partially transparent mirror or pellicle, and hence, with respect to the ballistic trajectory of the bullet. This is because the plays existing in the switching mechanisms with the moveable reticles or reticle elements cannot provide aforementioned positioning accuracy.
It is an object of the invention is to provide an optical sight for use in viewfinders of photocameras, or in aiming devices of fire arms, which is simple in construction, inexpensive to manufacture, has no moving parts, and ensures selection of reticle types and images in a wide range in compliance with the shooting conditions.